Comparison with other residual stress measurement methods
The figure at right shows the depth ranges of various methods compared
with (1) the depth of residual stresses produces by common manufacturing
processes and (2) the depth ranges where residual stresses would likely
contribute to failure mechanisms.
Crack compliance spans a very nice range of depths.
Plusses and minuses of various techniques:
This is the only method that can measure variation with depth nondestructively,
- It has limited resolution since it averages residual stress over
a volume. For example, in our ring test the
stresses of interest occurred in the first 1 mm of depth - which is
difficult for neutrons to resolve.
- You need to bring your part to a neutron source, i.e., a reactor
or a spallation source.
- Microstructural changes can make measurements difficult. Welds are
- This is nondestructive for measuring surface residual stresses.
- If you want to measure stress variation with depth you have to etch
away layers, which is very time consuming.
- It won't work on non-crystalline materials (neither will neutrons)
and is sensitive to grain size and texturing.
- Lack of sensitivity - the strains for a given residual stress distribution
are much lower than for compliance.
- You can only measure stresses to a limited depth whereas crack compliance
can measure through-thickness.
Crack Compliance (Slitting)
- All the methods above measure both residual stress components in
the surface plane, compliance only measures the component normal to
the face of the cut.
- If you are cutting into a tensile residual stress field, it is possible
for the crack to propagate. It doesn't happen often but it has happened.
- The contour method measures a full 2D stress map over the cross-section of a part. Slitting (Crack Compliance) is only 1D
- However, it is less sensitive than slitting, so not as good for very low magnitude stresses.
Deep Hole Drilling
- Measures all the way through very thick parts
- Measures all three stress components in the plane. Slitting and contour only measure the component normal to the cut plane.